PROCESS FOR PRODUCING ALKYL SULFONIC ACID

Abstract

The invention relates to a process for producing alkyl sulfonic acid in a reaction apparatus (41) which contains a liquid phase comprising aqueous nitric acid, wherein dialkyl disulfide is fed into the liquid phase in the reaction apparatus (41) and a crude reaction product is formed in the reaction apparatus (41) by chemical reaction of the dialkyl disulfide with the nitric acid, wherein feeding the dialkyl disulfide comprises at least one of: the liquid dialkyl disulfide is fed into the reaction apparatus (41) through an orifice (28, 29; 33) having a hydraulic diameter of less than 5 mm; the liquid dialkyl disulfide is fed into the reaction apparatus (41) with an inlet velocity of at least 0.6 m/s.

Claims

1. A process for producing alkyl sulfonic acid in a reaction apparatus comprising a liquid phase comprising aqueous nitric acid, the method comprising feeding dialkyl disulfide submerged into the liquid phase in the reaction apparatus and forming a crude reaction product in the reaction apparatus by chemical reaction of the dialkyl disulfide with the nitric acid, wherein feeding the dialkyl disulfide comprises at least one of: feeding the liquid dialkyl disulfide into the reaction apparatus through an orifice having a hydraulic diameter of less than 5 mm; and/or feeding the liquid dialkyl disulfide into the reaction apparatus with an inlet velocity of at least 0.6 m/s.

2. The process according to claim 1, wherein the reaction apparatus comprises a first reactor into which the liquid dialkyl disulfide and the nitric acid are fed and in which a first crude reaction product is formed, and a second reactor into which the first crude reaction product is fed and in which the reaction for forming the alkyl sulfonic acid is completed, thereby forming the crude reaction product.

3. The process according to claim 1, wherein the crude reaction product is worked-up to obtain a pure alkyl sulfonic acid.

4. The process according to claim 3, wherein working-up the crude reaction product comprises at least one distillation step.

5. The process according to claim 1, wherein the reaction apparatus comprises a reactor with an external fluid circulation.

6. The process according to claim 5, wherein the dialkyl disulfide is fed into the external fluid circulation.

7. The process according to claim 1, wherein the reaction apparatus comprises a jet loop reactor.

8. The process according to claim 1, wherein the reaction apparatus comprises a tank reactor.

9. The process according to claim 8, wherein the dialkyl disulfide is fed into the tank reactor through a plurality of orifices at the bottom and/or the walls of the tank reactor, through a dip tube having at least one opening, or through a distributor having a plurality of orifices.

10. The process according to claim 1, wherein the liquid dialkyl disulfide is fed into the reactor through a plurality of orifices, wherein the number of orifices is larger than 1.0 orifices per cubic meter reaction volume.

11. The process according to claim 1, wherein the reactor comprises an additional mixing device.

12. The process according to claim 1, wherein the dialkyl disulfide is dimethyl disulfide or diethyl disulfide and the alkyl sulfonic acid is methyl sulfonic acid or ethyl sulfonic acid.

Description

IN THE FIGURES

[0041] FIG. 1 shows a schematic flow chart of a process for producing alkyl sulfonic acid;

[0042] FIG. 2 shows a tank reactor with orifices at the bottom and the walls of the reactor;

[0043] FIG. 3 shows a tank reactor with a distribution ring for feeding the dialkyl disulfide;

[0044] FIG. 4 shows a reactor with an external fluid circulation with supply for dialkyl disulfide in the reactor;

[0045] FIG. 5 shows a reactor with an external fluid circulation with supply for dialkyl disulfide in the external fluid circulation;

[0046] FIG. 6 shows a schematic flow chart of the experimental set-up

[0047] FIG. 1 shows a schematic flow chart of a process for producing alkyl sulfonic acid.

[0048] For producing alkyl sulfonic acid, particularly methanesulfonic acid, nitric acid is fed into a reaction apparatus 41 via a first feed line 2 and dialkyl disulfide is fed into the reaction apparatus 41 via a second feed line 3.

[0049] The reaction apparatus 41 may comprise only one reactor or more than one reactor, for example two reactors.

[0050] The nitric acid fed into the reaction apparatus 41 preferably has a concentration from 20 to 100% by weight, more preferred from 40 to 70% by weight and particularly from 50 to 70% by weight, and the dialkyl disulfide preferably is pure dialkyl disulfide having a purity of greater than 98%. The molar ratio of dialkyl disulfide:nitric acid preferably is in a range from 1:2 to 1:20, more preferred in a range from 1:3 to 1:10 and particularly in a range from 1:3 to 1:6.

[0051] The reaction usually is carried out at a temperature in the range between 50 C. to 150 C., preferably at a temperature in the range from 80 C. to 140 C. and at an operating pressure in the range from 500 mbar to 8 bar, preferably at atmospheric pressure. Gaseous components obtained in the reaction, which comprise nitrogen oxides like nitrogen monoxide and nitrogen dioxide, are transferred to a nitric acid regeneration system 39 via a gas line 7.

[0052] The liquid crude reaction product obtained in the reaction apparatus 41 is fed into a distillation 40 via a transfer line 8. In the distillation 40, the liquid crude reaction product is separated into a light fraction 25, a mid-boiler fraction 23, comprising the pure methanesulfonic acid and a bottom stream 22, which comprises high boilers.

[0053] The low boilers, which are obtained in the distillation 40 usually are condensed and the part which does not condense is withdrawn from the distillation 40 as light fraction 25. The condensed low boilers, which contain nitric acid, are partly transferred back into the distillation 40. That part of the condensed low boilers which is not transferred back into the distillation 40 is transferred to the nitric acid regeneration system 39.

[0054] The distillation 40 may comprise only one distillation column or, preferably, at least two distillation columns. If the distillation 40 comprises one distillation column, the light fraction 25 is withdrawn from the top of the column, the mid-boiler fraction 23 by a side take-off and the high boilers at the bottom of the column. If two distillation columns are used, in the first distillation column the high boilers and mid-boilers are separated and withdrawn at the bottom of the first distillation column and low boilers are withdrawn at the top of the first distillation column and transferred into the nitric acid regeneration system 39. The mid-boilers and the high boilers withdrawn at the bottom of the first distillation column are transferred into a second distillation column in which the high boilers are withdrawn at the bottom of the column as bottom stream 22, the mid-boiler fraction 23 comprising the pure alkane sulfonic acid is withdrawn as a side stream from the second distillation column and the light fraction 25 comprising remaining low-boilers is withdrawn at the top of the second distillation column.

[0055] For regenerating the nitric acid, besides the gaseous phase obtained in the reaction apparatus 41 and the condensed part of the low boilers of the distillation 40, air 43 and water 44 are fed into the nitric acid regeneration system 39. In the nitric acid regeneration system 39, the nitric acid transferred from the distillation 40 is concentrated and the nitrogen oxides, which are obtained in the reaction react with the water, thereby forming nitric acid. To compensate losses of nitric acid, fresh nitric acid can be added to the system via line 45.

[0056] Different embodiments of reactor configurations carrying out the inventive process are shown in FIGS. 2 to 5. If the reaction apparatus 41 comprises a series of reactors for carrying out the inventive process, all the reactors may have a similar construction, but it is also possible to use different reactor designs for a series of reactors. For example in a series of two reactors, the first reactor may be a stirred tank reactor and the second reactor may be a tank reactor with an external fluid circulation line.

[0057] FIG. 2 shows a tank reactor with orifices at the bottom and the walls of the reactor.

[0058] In the embodiment shown in FIG. 2, the reactor 1 is a tank reactor to which the first feed line 2 for feeding nitric acid is connected. For withdrawing the crude reaction product, the tank reactor comprises transfer line 8, and for removing evaporated low boilers and gaseous components, the gas line 4 is connected to the top of the tank reactor.

[0059] For feeding the dialkyl disulfide, the second feed line 3 is connected to orifices 28 at the bottom of the tank reactor and to orifices 29 at the walls of the tank reactor. The orifices 29 at the walls of the tank reactor are at such positions at the walls, that all orifices 29 at the walls of the tank reactor are placed below the liquid/gas phase boundary in the liquid phase. The orifices 28 at the bottom and orifices 29 at the walls of the reactor have a hydraulic diameter of less than 5 mm. Additionally, the amount of orifices 28 at the bottom and of orifices 29 at the walls is such that the number of orifices is larger than 1.0 orifices per cubic meter reaction volume.

[0060] The tank reactor may be an unstirred tank reactor or a stirred tank reactor. If the tank reactor is a stirred tank reactor, the tank reactor comprises a mixing device 30. As the mixing device 30 only is optional, it is shown in FIG. 2 with a dashed line. The mixing device 30 may be any type of stirrer known to the skilled person and as described above.

[0061] The crude reaction product is withdrawn from the reactor 1 via the transfer line 8 and gaseous components via a gas line 4.

[0062] FIG. 3 shows a tank reactor with a distribution ring for feeding the dialkyl disulfide.

[0063] The tank reactor, which is shown in FIG. 3, differs from the tank reactor shown in FIG. 2 in the feeding device for the dialkyl disulfide.

[0064] In contrast to the tank reactor shown in FIG. 2, the second feeding line 3 of the tank reactor of FIG. 3 is a dip tube 31 which is connected to a distributor 32. In the distributor 32, orifices 33 are formed for feeding the dialkyl disulfide. As the orifices 28, 29 in the bottom and wall of the tank reactor shown in FIG. 2, each orifice 33 has a hydraulic diameter of less than 5 mm and the number of orifices 33 in the distributor 32 is larger than 1.0 orifices per cubic meter reaction volume.

[0065] A further alternative for the reactor construction is shown in FIG. 4.

[0066] According to the embodiment shown in FIG. 4, the reactor 1 is a tank reactor with an external fluid circulation 34. In the reactor shown here, the first feed line 2 for feeding the nitric acid opens into the external fluid circulation 34. For circulating the liquid phase, a pump 35 is arranged in the external fluid circulation 34. The pump 35 may be any suitable pump for circulation of the liquid or gas liquid mixture, for example a centrifugal pump. The external fluid circulation 34 ends in an ejector nozzle 36 through which the liquid is injected into the tank reactor. The second feed line 3 for feeding the dialkyl disulfide ends in the ejector nozzle 36 and the dialkyl disulfide is sucked through the ejector nozzle into the liquid jet which leaves the nozzle. According to the invention, the liquid dialkyl disulfide is fed into the nozzle with an inlet velocity of at least 0.6 m/s. The mixture exiting the nozzle preferably is introduced into the tank contents below the liquid surface to prevent the formation of an explosive gas mixture. To generate a loop flow in the tank reactor, at least the nozzle outlet is surrounded by an inner tube 46. By injecting the liquid into the tank reactor via the ejector nozzle 36 the liquid flows through the inner tube 46 to a first end 47, surrounds the first end 47 of the inner tube 46 and flows outside of the inner tube 46 in the opposite direction to a second end 48 of the inner tube 46 and then into the inner tube 46 again. By this, the loop flow is generated in the reactor by which the components are mixed.

[0067] A reactor with an external fluid circulation with supply for dialkyl disulfide in the external fluid circulation is shown in FIG. 5.

[0068] As in the reactors shown in FIGS. 2 and 3, the nitric acid is fed directly into the reactor via the first feed line 2.

[0069] In contrast to the reactor shown in FIG. 4, the second feed line 3 for feeding the dialkyl disulfide is connected to a nozzle 37 which is placed in the external fluid circulation 34. By using the nozzle 37, the dialkyl disulfide is fed into the external fluid circulation 34 such that the inlet velocity of the liquid jet leaving the nozzle 37 and, thus, also the inlet velocity of the dialkyl disulfide is at least 0.6 m/s.

[0070] To further mix the liquid in the external fluid circulation 34 and the dialkyl disulfide, it is preferred to provide a static mixer 38 in the external fluid circulation 34 downstream the nozzle 37.

EXAMPLES

[0071] A setup according to FIG. 6 and to the following description was used for all examples given below. The inventive process was performed in the set up as follows, in which the reaction apparatus 41 comprises a first reactor 1.1 and a second reactor 1.2: For producing alkyl sulfonic acid, particularly methanesulfonic acid, nitric acid is fed into a first reactor 1.1 via the first feed line 2 and dialkyl disulfide is fed into the first reactor 1.1 via the second feed line 3.

[0072] Due to the reaction conditions in the first reactor 1.1, at least some of the low boilers contained in the first reactor 1.1, for example nitric acid and water, evaporate and are withdrawn together with gaseous by-products from the first reactor 1.1 via a gas line 4 and fed into a first condenser 5. In the first condenser 5, condensable components condense and are fed back into the first reactor 1.1 via a recycle line 6. The non-condensed components, which comprise nitrogen oxides like nitrogen monoxide and nitrogen dioxide, are transferred to the nitric acid regeneration system 39 via a gas line 7. Preferably, the nitric acid obtained in the nitric acid regeneration system 39 is recycled into the process and fed into the first reactor 1.1 via the first feed line 2. Fresh nitric acid can be added via line 45 to compensate nitric acid losses.

[0073] From the first reactor 1.1 a stream is withdrawn via a transfer line 8 and fed into a second reactor 1.2.

[0074] As in the first reactor 1.1, gaseous by-products are formed and low boilers partially evaporate in the second reactor 1.2. The evaporated low boilers and gaseous by-products, like nitrogen oxides, are withdrawn via a gas line 10 and fed into the second condenser 11. In the second condenser 11 the condensable low boilers condense. The condensed low boilers, which contain nitric acid, are transferred to the regeneration for nitric acid via a feed line 12 and the non-condensed components comprising nitrogen oxides are transferred to the regeneration for nitric acid via a gas line 13.

[0075] The liquid crude reaction product obtained in the second reactor 1.2 is fed into a first distillation column 15 via a transfer line 14. In this first distillation column 15 light boilers are evaporated and condensed in a third condenser 16. The reflux 17 from the third condenser 16 is divided and transferred back to the head of column 15 or transferred to the nitric acid regeneration system 39. The concentrated bottom stream is heated in a first reboiler 19 and part of the bottom stream is transferred via a line 18 to a second distillation column 20. In the second distillation column 20, the stream from the line 18 is split into a top stream 21, a mid-boiler fraction 23, comprising the pure methanesulfonic acid and a bottom stream 22. The top stream 21 of the distillation column 20 is condensed in a fourth condenser 24 and part of the stream is withdrawn as the light fraction 25, whereas the rest of the condensed stream 21 is recirculated to the head section of the second distillation column 20. From the bottom stream 22 a purge stream 27 is branched off, before the stream is heated in a second reboiler 26 and recirculated to the bottom of the second distillation column 20.

Example 1

[0076] The first reactor 1.1 was charged continuously, while continuously agitated, via the second feed line 3 with pure dimethyl disulfide (>98%) and with 55-65% strength nitric acid via feed line 2 in the DMDS (dimethyl disulfide): HNO3 molar ratio of 1:5,3.

[0077] Dimethyl disulfide is introduced submerged into the reaction mixture in the first reactor 1.1 via a distribution ring.

[0078] The distribution ring has 1.7 orifices per cubic meter of reaction volume in the first reactor 1.1. An agitator is mounted below the distributor ring. The orifices are spread evenly around the distributor ring. The exit velocity of DMDS through the orifices is 0.63 m/s and the diameter of the orifices is 5 mm.

[0079] The temperature in the first reactor 1.1 is about 100 C. The residence time in the first reactor 1.1, calculated as a quotient of the liquid volume in the first reactor 1.1, divided by the liquid stream which is continuously leaving the first reactor 1.1 through transfer line 8, is about 3.2 h.

[0080] The NO.sub.x-containing offgas stream formed in the first reactor 1.1 and freed from condensable components in the first condenser 5 comprises NO and NO.sub.2 and is passed to the nitric acid regeneration system 39.

[0081] The liquid stream which is continuously leaving the first reactor 1.1 is fed to the second reactor 1.2 via the transfer line 8. The temperature in the second reactor 1.2 is about 130 C. The residence time in the second reactor 1.2, calculated as a quotient of the liquid volume in the second reactor 1.2, divided by the liquid stream which is continuously leaving the second reactor 1.2 through transfer line 14, is about 3.5 h.

[0082] The NO.sub.x-containing offgas stream formed in the second reactor 1.2 is freed from condensable components in the second condenser 11. The offgas stream leaving the second condenser 11 comprises NO and NO.sub.2 and the condensate leaving the second condenser 11 comprises nitric acid. Both streams are passed to the nitric acid regeneration system 39.

[0083] The liquid stream which is continuously leaving the second reactor 1.2 is passed to the first distillation column 15 via transfer line 14. The first distillation column 15 is operated at a head pressure of from 85 to 100 mbar(abs) and a bottom temperature of 170 to 180 C.

[0084] The bottom product of the first distillation column 15, which comprises alkyl sulfonic acid as main component and high boilers like sulfuric acid is withdrawn from the first distillation column 15 as a bottom stream 18 and, after a part of the bottom stream 18 is branched off, fed into a second distillation column 20.

[0085] The part of the bottom stream 18 which is branched off, is heated in a heat exchanger 19 and recycled into the bottom part of the first distillation column 15.

[0086] The condensate obtained in the condenser 16 with reflux divider contains nitric acid and is fed to the nitric acid regeneration system 39.

[0087] In the second distillation column 20, which is operated with a head pressure in the range from 5 to 10 mbar(abs) and a bottom temperature in the range from 180 to 190 C., the bottom stream of the first distillation column 15 is separated into the top stream 21 comprising low boilers, which is withdrawn at the head of the second distillation column, a bottom stream 22 comprising high boilers, and the mid-boiling fraction 23 comprising pure alkyl sulfonic acid as product stream. The mid-boiling fraction 23 is withdrawn from the second distillation column 20 as a side stream.

[0088] The mid-boiling fraction 23 leaving the second distillation column 20 consists of >99.5% strength methanesulfonic acid having a sulfuric acid content of <50 ppm.

[0089] The top stream 21 is fed into a condenser 24 with reflux divider, in which the top stream is condensed, and a part of the top stream is recycled into the head section of the second distillation column 20 and the rest of the condensed top stream is withdrawn from the process as light fraction 25. The light fraction 25 leaving the second distillation column 20 consists of water, methanesulfonic acid, methyl methanesulfonate and other low-boiling components.

[0090] The bottom stream is divided into a first partial stream which is fed into a heat exchanger 26, in which the first partial stream is heated, and a second partial stream, which is withdrawn from the process as purge stream 27. After heating, the first partial stream is recycled into the second distillation column 20.

[0091] The purge stream 27 leaving the second distillation column 20 contains sulfuric acid, methanesulfonic acid and other high-boiling components.

[0092] The bottom product leaving the first distillation column 15 contains: [0093] methanesulfonic acid: 97.7 wt % [0094] water: 1.6 wt % [0095] sulfuric acid: 0.3 wt %

Example 2

[0096] The reaction was performed in the same set-up as described as in example 1. The process parameters were as described as in example 1, but in this case DMDS was distributed with an exit velocity of DMDS through the nozzles of 1.76 m/s and the nozzle diameter is 3 mm.

[0097] The bottom product leaving the first distillation column 15 contains: [0098] methanesulfonic acid: 97.9 wt % [0099] water: 1.6 wt % [0100] sulfuric acid: 0.2 wt %

[0101] A comparison of examples 1 and 2 shows that by reducing the diameter of the nozzles and increasing the exit velocity, the amount of sulfuric acid can be reduced by one third.

Example 3

[0102] The reaction was performed in experimental set-up 2 which is also according to FIG. 6.

[0103] The first reactor 1.1 was charged continuously, while continuously agitated, via the second feed line 3 with pure dimethyl disulfide (>98%) and with 55-65% strength nitric acid in the DMDS (dimethyl disulfide): HNO3 molar ratio of 1:5.1.

[0104] Dimethyl disulfide is introduced submerged into the liquid phase in the first reactor 1.1 via a distribution ring.

[0105] The distribution ring has 1.2 orifices per cubic meter of reaction volume in the first reactor 1.1. An agitator is mounted below the distributor ring. The orifices are spread evenly around the distributor ring. The exit velocity of DMDS through the orifices is 2.51 m/s and the diameter of the orifices is 3 mm.

[0106] The temperature in the first reactor 1.1 is about 100 C. The residence time in the first reactor 1.1, calculated as a quotient of the liquid volume in the first reactor 1.1, divided by the liquid stream which is continuously leaving the first reactor 1.1 through transfer line 8, is about 2.7 h.

[0107] The NO.sub.x-containing offgas stream formed in the first reactor 1.1 and freed from condensable components in the first condenser 11 comprises NO and NO.sub.2 and is passed to the nitric acid regeneration system 39.

[0108] The liquid stream which is continuously leaving the first reactor 1.1 is fed to the second reactor 1.2 via the transfer line 8. The temperature in the second reactor 1.2 is about 130 C. The residence time in the second reactor 1.2, calculated as a quotient of the liquid volume in the second reactor 1.2, divided by the liquid stream which is continuously leaving the second reactor 1.2 through transfer line 14, is about 3.2 h.

[0109] The NO.sub.x-containing offgas stream formed in the second reactor 1.2 is freed from condensable components in the second condenser 11. The offgas stream leaving the second condenser 11 comprises NO and NO.sub.2 and the condensate leaving the second condenser 11 comprises nitric acid. Both streams are passed to the nitric acid regeneration system 39.

[0110] The liquid stream which is continuously leaving the second reactor 1.2 is passed to the first distillation column 15. The first distillation column 15 is operated at a head pressure of from 85 to 100 mbar(abs) and a bottom temperature of 170 to 180 C. The bottom product leaving the first distillation column 15 is transferred to the second distillation column 20.

[0111] The condensate obtained in the third condenser 16 with reflux divider contains nitric acid and is fed to the nitric acid regeneration system 39.

[0112] The mid-boiling fraction 23 leaving the second distillation column 20 as side stream consists of >99.5% strength methanesulfonic acid having a sulfuric acid content of <50 ppm. The light fraction 25 leaving the second distillation column 20 consists of water, methanesulfonic acid, methyl methanesulfonate and other low-boiling components.

[0113] The purge stream 27 leaving the second distillation column 20 consists of sulfuric acid, methanesulfonic acid and other high-boiling components.

[0114] The bottom product leaving the first distillation column 15 contains: [0115] methanesulfonic acid: 97.0 wt % [0116] water: 2.0 wt % [0117] sulfuric acid: 0.3 wt %

Example 4

[0118] The reaction was performed in the same set-up as described as in example 3. The process parameters were as described as in example 3, but in this case DMDS was distributed with a distributor ring with 1.7 nozzles per cubic meter of reaction volume and an exit velocity of DMDS through the nozzles of 7.45 m/s and the diameter of the orifices is 1.5 mm.

[0119] The bottom product leaving the first distillation column 15 contains: [0120] methanesulfonic acid: 97.2 wt % [0121] water: 2.0 wt % [0122] sulfuric acid: 0.2 wt %

[0123] By the comparison of the composition of the bottom product leaving the first distillation column 15 of examples 3 and 4, it can be seen that by reducing the diameter of the orifices and increasing the exit velocity of the DMDS, as well as increasing the amount of orifices per reaction volume, the amount of sulfuric acid can be reduced further.

Example 5

[0124] The reaction was performed in the same set-up as described in example 3. However, in this case the exit velocity of DMDS through the nozzles is 1.27 m/s. The residence time in the first reactor 1.1 was increased from 2.7 h to 5.2 h and in the second reactor 1.2 from 3.2 h to 6.3 h. All other process parameters were as described in example 3.

[0125] The bottom product leaving the first distillation column 15 contains: [0126] methanesulfonic acid: 97.1 wt % [0127] water: 2.0 wt % [0128] sulfuric acid: 0.3 wt %

[0129] The comparison with the results from example 3 shows that a reduced exit velocity of DMDS of 1.27 m/s and a longer residence time in the first reactor 1.1 and the second reactor 1.2 has no effect on formation of sulfuric acid.

Comparative Example

[0130] The reaction was performed in the same set-up as described in example 1. The process parameters were as described as in example 1, but in this case DMDS was distributed with an exit velocity of DMDS through the nozzles of 0.41 m/s and the nozzle diameter is 5 mm.

[0131] The residence time in the first reactor 1.1 was increased from about 3.2 h to about 4.5 h and in the second reactor 1.2 from about 3.5 h to about 5.4 h. All other process parameters were as described in example 1.

[0132] The bottom product leaving the first distillation column 15 contains: [0133] methanesulfonic acid: 97.7 wt % [0134] water: 1.7 wt % [0135] sulfuric acid: 0.4 wt %

[0136] A comparison of example 1 and the comparative example shows that by reducing the exit velocity through the orifices below 0.63 m/s the amount of sulfuric acid that is produced increases significantly.

TABLE-US-00001 List of reference numbers 1 reactor 1.1 first reactor 1.2 second reactor 2 first feed line 3 second feed line 4 gas line 5 first condenser 6 recycle line 7 gas line 8 transfer line 10 gas line 11 second condenser 12 feed line 13 gas line 14 transfer line 15 first distillation column 16 third condenser 17 reflux 18 line 19 first reboiler 20 second distillation column 21 top stream 22 bottom stream 23 mid-boiler fraction 24 forth condenser 25 light fraction 26 second reboiler 27 purge stream 28 orifices at the bottom of the reactor 29 orifices at the wall of the reactor 30 mixing device 31 dip tube 32 distributor 33 orifice 34 external fluid circulation 35 pump 36 ejector nozzle 37 nozzle 38 static mixer 39 regeneration for nitric acid 40 distillation 41 reaction apparatus 43 air 44 water 45 nitric acid 46 inner tube 47 first end 48 second end